Remote control system



1939 c. s. SNAVELY ET AL 2,133,155

REMOTE CONTROL SYSTEM Filed y 16 35 5 Sheets-Sheet 2 Office 0R5 Szorage 012658 45 INVENTORS Clarence S. Snauely red B. Miler SAPLhaPPJqchel BY 61 32 z/TM a THEIR ATTORNEY Fig. 2.

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BY @KLW THEIR ATTORNEY Patented Dec. 12, 1939 I Z,l3,l55

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2,183,155 REMOTE CONTROL SYSTEM Clarence S. Snavely, Swissvale, Alfred B. Miller, Edgewood, and Arthur P. Jackal, Swissvale, Pa, assignors to The Union Switch & Signal Conipany, Swissvale, Pa., a corporation of Pennsylvania Application July 16, 1935;, Serial No. 3 1,592

88 Claims.

Our invention relates to remote control systems for the control from a central point. of selected devices located at remote points, and also for indicating at the control point the condition of such devices and of other devices located at remote points. In its specific embodiment, our invention relates particularly to centralized traffic control systems for. railroads,3of the type in which a large number of railway signals and track switches at more or less widely spaced field stations are controlled from time to time'from a dispatchers oficeover a single line circuit, and in which the same line circuit is employed at other times to indicate at the dispatchers office the positions assumed by the switches and signals, or to indicate traffic conditionsat the same or at other field stations.

Our invention contemplates the use of code signals produced by interrupting a normally closed line circuit connecting the dispatchers office and the several stations, and more specifically, employs a code in which the period of open circuit and closed circuit in the line are both varied so that both of-these periods constitute code elements, as disclosed and claimed in a copending application of Lloyd V, Lewis, Serial No. 6d0,786, filed March 23, 1932, for Remote control systems.

One object of our invention is the provision of a system employing a code of time-spaced elements in which selected elements are prolonged ior different time intervals, so that each code element may have one of at least three possible characters. For example, in the codes utilized by our apparatus as herein disclosed, each code element may be short, medium, or long, and our apparatus provides a large number of different codes while employing but one line circuit and a relatively small number of code elements, and in respect to this feature, our apparatus is an improvement upon that disclosed and claimed in the copending application of Snavely, Miller and Tunell, SerialNo. 538,380, filed May 18, 1931, for Remote control systems. v

Another object of our invention is to provide a line circuit which does not require the sectionalising devices heretofore employed in systems of this character, andour apparatus functions in such a manner as to permit the control office to be located either at the end or at any desired intermediate point in the line circuit, the differ ent codes being transmitted one at a time in the proper order even though two stations or the ofiice and a station start to transmit at the same time.

Another object of our invention resides in the provision of means for electrically interlocking the apparatus for controlling the transmission of the different control codes from the dispatchers office in such a manner as to insure the transmission of a series of codes for effecting a sequence of related operations in a predetermined order, and to also prevent the transmission of certain codes when the devices controlled 1y such codes are locked against operation.

Other objects and features of our invention nice coding unit, includes the dispatchers ofiice equipment for generating and delivering different codes to the line circuit of the system and for receiving and decoding the codes received over the line circuit from the field stations. Fig.

2, entitled oflice storage units shows, at the left, an apparatus unit such as is used to control each track switch of the system and to indicate the condition of the track switch and of an adjacent track section, At the right, Fig. 2 shows a different apparatus unit such as is used to control a group of signals and to indicate condition of the signals and of an adjacent track section, this unit including an auxiliary unit for the control of a slow-speed or call-on signal. Fig. 3, en-

tled station coding unit includes the group of apparatus located at each station which corresponds in function to, the ofiice equipment of Fig. 1. Fig. 4 entitled station storage units, shows the apparatus units located at each station which cooperate with the corresponding units of Fig. 2 to. eiiect the control of the switch and signals at the stations'and to govern the transmission of indications from the station. Fig. 5 is a track diagram showing the arrangement of the switches and signals in a typical small interlocking. Fig. 6 illustrates a modification of the signal lever circuits of 2 which serves to electrically interlock the. signal levers when our apparatus is employed to control'interlockedsignals arranged as in Fig. 5. Fig. 7

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illustrates a corresponding modification of the switch lever circuits of Fig. 2 which may be used when the switches of Fig. 5 are controlled by our apparatus, Fig. 8 is a track diagram showing a typical arrangement of switches and signals for governing the movement of trafiic on a single track railroad. Fig. 9 illustrates a modification of the signal lever circuits of Fig. 2 which serves to interlock the signal lever circuits for the signals at adjoining stations when the signals are arranged as shown in Fig. 8. Fig. 10 shows the line circuit by which the apparatus of Figs. 1 and 3 is interconnected when the system is arranged to control the switches and signals of Figs. 5 and 8 from a centrally located office.

Similar reference characters refer to similar parts in each of the several views.

The line circuit employed in systems embodying our invention comprises a single control Wire and a common return wire. Referring to Figs. 1 and 3, each coding unit has a pair of line terminals X and Y, and the line circuit is formed as indicated in Fig. 10, by connecting each terminal Y to the terminal X of another unit to form a closed circuit, a line battery Iii being included in the circuit at any convenient point. The line circuit is normally closed and includes at the oflice and at each station, a normally energized line relay designated by the reference R with a prefix identifying the location, and a back contact l of a similarly identified transmitter relay T. When any transmitter relay T is operated to deliver a code to the line circuit, the line relays R operate in unison and control the several operations involved in the generation of the line signals at the sending point and in the decoding of the line signals at the receiving point.

The line battery it) is proportioned according to the number of stations and the length and resistance of the line wires, and while it is usually convenient to locate it at the omce, as indicated, it may be sub-divided and portions located at diiferent points in order to minimize the effect of line leakage and thereby increase the number of stations and extent of territory controlled. Sparking of the contacts in the line circuit is avoided by connecting across each relay R a resistor I l and a condenser l2, in series, these parts being proportioned so as to absorb the inductive energy of the relay when the line circuit is opened.

In order to simplify our drawings and to avoid duplication of parts in different views, we have shown but one of each of the several units employed in systems embodying our invention, and the apparatus of Figs. 1 to 4, inclusive, taking but one copy of each sheet, forms a complete system arranged to control from a remote ofiice a single switch such as switch [SW of Fig. 8, and the opposing signals R2 and L2 for governing the movement of trafdc in opposite directions over the switch. This system is also arranged to automatically indicate at the office the condition of the switch iSW, oi' the signals L2 and R2, of a track section such as the section IDT containing the switch, and of another track section such as the adjacent approach section IAT.

For simplicity our apparatus will be explained with reference to this simple layout, and it will then be pointed out how the drawings may be expanded by a duplication of certain portions so as to illustrate each detail of more extensive systems including a plurality of stations and a plurality of interlocked switches and signals at a station.

Before proceeding with a detailed description of the circuits, however, we will briefly explain the general plan and organization of a typical centralized traffic control system embodying the apparatus of our invention.

As herein illustrated, in each code the line is opened and closed four times, each code including seven elements. The timing of the successive code elements is controlled by a group of slowrelease timing relays MO, MC and L controlled by a line relay R. Relay MO is deenergized when the line is open and relay R is released, and measures the medium line-open code elements. Relay MC is deenergized when the line is closed and relay R picked up, and measures the medium line-closed code elements, while relay L is a repeater of relays MO and MC and measures the long code elements. Relays R, MO and L, or relays R, MC and L, as the case may be, function in such a manner as to close a series of contacts one at a time at spaced intervals when the line relay remains in the corresponding position. These relays control two slow-release bridging relays LB and LBP which control various local circuits and also serve to space consecutive codes and to insure that a code will not be transmitted except when the line circuit is available. The timing relays alternately control two groups of iegisterreiays SOR, MOR, LOR and SCR, MCR, LCR to register the short, medium or long lineopen or line-closed code elements respectively. A p1 eliminary stepping relay, designated by the reference GP in Fig. 1 and by the reference IP in Fig. 3, picks up when the line opens at the beginning of the code, and controls the first of a series of stepping relays similarly distinguished by the prefix O or I and bearing the references A, B, C, D, E and F. These relays are operated one at a time, each at the end of a different code element, but with the exception of relay A, only if such element has a particular one of the three possible characters. As illustrated, there are three relays Fl, F2 and F3, one for each different character of the sixth element, each of which is adapted to control a selected three-position device in accordance with the character of the seventh element. When arranged with five selecting elements as herein illustrated, our apparatus therefore provides 3 3 3 3 3 43 different codes for the control of three-position devices.

All of the apparatus so far described operates in unison at the office and station, both in sending control codes from the office to the station and in sending indication codes from the station to the ofiice, but each coding unit includes a master relay MR, which is energized to cause the coding unit to function as a transmitter, and differentiates between the sending and receiving functions of the coding unit.

Each control code transmitted from the oiiice to a station is differentiated from the corresponding indication code by the character of the first element, which is long in each control code and of difierent character in each indication code. At the beginning of the second element of each indication code a register relay TC or T0 is picked up, depending upon whether the first element is short or medium, to register the condition of a track circuit at the station, each indication code thus being adapted to indicate the condition of one two-position and one three-position device.

When relay MR is energized, the transmitter relay T is operated repeatedly to generate the code under the control of an auxiliary relay CT and a polar relay PT, which relays are controlled by circuits governed by the timing and'stepping relays. An individual code sending relay CS is provided for each code, which functions to pick up relay MR to initiate the code and to determine the character of the selecting elements. Each relay CS is controlled by an associated storing relay S. A knock-down key ED is provided by means of which the omce relays CS and S may be released manuallyii due to some irregularity the coding unit is unable to complete a code.

'As herein illustrated, the control code which selects the stepping relays OFl and UN is employed to operate a switch control relay WS for governing the operation of the track switch, this code being transmitted in response to an opera tion of a two-position switch lever W at the ofiice.

' A normally energized lever relay Ni releases to initiate the code whenever leverW is moved, the

release of relay N! causing a storing relay Si to become energized to operate the corresponding code sending relay but only if conditions as refiected by the indication and signal control apparatus at the office are favorable for the operating of the switch, so that a lock relay WLI is energized. The character of the seventh element of a switch control code is determined by a stick polar relay Pi which moves to aposition corresponding to that of the st itch lever when the lever is operated, but only if conditions are favorable for sending the code, and the code is transmitted only when lever "W5 and relay P! occupy corresponding positions.

The switch control relay WS controls a switch operating relay WE. over circuits including contacts of approach locking relays LMR and RMR and of the track relay TR for the switch section. The circuits for the last-mentioned relays have been omitted to simplify the drawings, since they are not part of the present invention, but it is to be understood that they may be arranged,

for example, as disclosed in the Kemmerer Patent No. 1,885,521, issued November 1, 1932, for Railway traffic controllin apparatus, so as to locally look the switch against operation under unfavorable conditions irrespective of the condition of relay WS.

The condition of the switch is indicated at'the office by a lamp WE associated with the lever. Lamp WE is normally dark but becomes lighted due to the release of a switch indication relay WK when a'code is transmitted to operate the track switch or when the switch becomes unlocked or displaced due to conditions in the field, and is extinguished by the re-energization of that relay when an indication code is received, indicating that the switch is locked in a position corresponding to that of relay Pl. Lamp WE displays a flashing indication when the lever is moved and relay Pl does not respond, indicating that the sending of the code is improper and that the lever should be returned to its original position. Indication relay AK is also controlled by the switch indication code and is operated to light the approach indication lamp AE whenever a code is received indicating that the corresponding approach section has become occupied.

As herein illustrated, the control code which selects the stepping relays OFZ and W2 is employed to control a pair of stick polar signal control relays LHS and RI-IS for governing the signals L2 and R2, and is transmitted in response to the operation of a three-position signal lever G. When this lever is moved to its mid-position, a

lever rela'y H2 is released to energize a storing relay S2, and then a lever relay N2 and a code sending relay CS2 become-energized to effect the transmission of a code to put the signals to stop. There is no restriction upon the transmission of this code which may be initiated at any time to be transmitted as soon as the line circuit becomes available. If lever G is moved to the left or right, relay N2 releases, to initiate a code to clear either signal L2 or R2 depending upon the.

if the contacts of an indication relay MK are closed. Relay-MK is operated to open its contacts when a signal clear code is transmitted, and to close its contacts upon receipt of an indication code from the station indicating that the signals have been put to stop and that the approach locking relays governed by the signals have become energized. These various arrangements serve to prevent the sending of a code to clear a signal unless the route governed by the signal has been aligned, the opposing signal has been put to stop, and the approach locking associated with that signal is released. Furthermore, a signal when cleared can not be interfered with by attempting to transmit conflicting codes.

Another feature of our apparatus resides in the provision of an auxiliary key NSK associated with lever (31. In normal operation, the signal control relays are operated automatically when a train enters'the switch section so as to cause the signal to. remain at stop after the train leaves the section, but if a signal is cleared and key NSK has been operated a signal clear contro1 code will be initiated automatically upon receipt or" a code indicating that a train has vacated the switch section, so that the signal will clear again for a following train, as explained hereinafter in detail. The condition of the signals is indicated by a lamp HE associated with lever G. Lamp HE is normally dark but becomes lighted by the operation of an indication relay l-IK in response to an indication code initiated by the release of a signal repeating relay LGP or RGP at the station, which relays may be controlled as disclosed in the abovementioned Kemmerer patent, each releasing when the corresponding signal is cleared. Lamp HE displays a flashing indication when the lever is operated and code-sending relay CS2 fails to become energized, indicating that the clearing of the signal is improper and can not be effected.

The flashing indications of lamps HE and WE are controlled by a pair of flasher relays ERA and PR2 which operate alternately whenever a hashing indication is to be displayed. Indication relay TK is also controlled by the signal indication code and is operated to light lamp TE whenever a code is received indicating that the switch sectionis occupied.

Our indication apparatus also includes an audible warning signal comprising a bell XB conis employed for the purpose of clearing an auxiliary slow speed or call-on signal such as arm 0 of signal R2, in the event a code has been transmitted to clear arm a or arm I), and the signal is prevented from clearing by traffic conditions. This code is initiated by picking up a code sending relay CS3 by the operation of a spring return key CO associated with lever G. Relay IFS controls a call-on signal relay CHS at the station, governing arm 0 of the signal for the established direction of trafiic. I

At the field station, the different devices govern the transmission of indication codes in a generally similar manner, the codes being initiated automatically by the successive energization of a starting relay such as iST or 2ST and a storing relay IS Or 23 when one or another of the indicating devices changes its position. The switch indication code is also initiated by the energization of relay is when a control code is received at the station, so that irrespective of whether the switch is operated or not, each switch control code is followed by a return indication. The character of the selecting elements of the indication codes is determined by the relays CS, while that of the indicating elements is determined by stick polar relays WV, AV, GV, MV and TV which reflect the condition of the various indicating devices. Thus relays WV and AV are controlled respectively by the switch indication relay KR controlled by the switch and by the track relay AR for an adjacent approach section such as section lAT of Fig. 8. Relay (3V is controlled by the signal indication relays LGP and RGP. Relay MV is controlled by a repeating relay MP which indicates the condition of the signal control relays and of the approach locking relays. Relay TV is controlled by an indication storing relay TS which in turn is controlled by a repeater relay TP of the track relay TR for a track section such as the switch section IDT of Fig. 8, the circuits being so arranged that in the event the switch section becomes occupied and vacated while the line is in use, the track occupied indication will be stored until the line becomes available for its transmission.

As will be apparent from the foregoing, our apparatus consists principally of an assembly of interconnected relays. Most of the relays are quickacting, but in a number of instances the relay circuits include asymmetric units designated by the reference 1' with numerical prefix. each of which is arranged in the circuit so as to provide a high resistance to the flow of current from the power source While providing a low resistance discharge path to permit the gradual discharge of the stored inductive energy of the relay or relays when the power source is disconnected so that no sparking occurs when the controlling contacts are opened. The release of these relays is thereby delayed somewhat, but the parts are so proportioned that their release period is much shorter than that of those relays indicated conventionally as slow-release relays on the drawings. The latter slow-release relays are all alike, and are constructed so as to open their front contacts at the end of a constant time period after the circuit is opened, under a wide variety of operating conditions. The stick polar relays herein disclosed each have two windings, and it is to be understood that each is arranged to move its contacts to the right when the righthand winding is energized and to the left when the left-hand winding is energized, and that the contacts are held positively in the last-operated position when the relay is deenergized.

A local direct current power source is provided at each location, but for simplicity these have been omitted and we have shown only the terminals of the sources and have designated these by the references B and C to indicate the power supply and common return terminals, respectively, of the sources. In some installations, rectified alternating current without a battery reserve is employed as the local power source, and since such a source may be subject to temporary interruption our apparatus is arranged so as to minimize the effect of such interruptions. To this end a relay LL is connected directly across terminals B and C of the local source and a front contact I of this relay is included in the line circuit, so that in the event of a failure of the local source, relay LL will release and open the line circuit, and the transmission of codes will be suspended until the local power is restored.

We will now describe, in detail, the various operations involved in reversing switch lSW and in clearing arm b of signal R2 by code. Assuming the apparatus to be in the condition shown in the drawings, it will be noted that in the coding units of Figs. 1 and 3, all of the relays are deenergized except the line relays R, the slow release relay MO, relay LL and the bell relay XR. The circuit for relay MO may be traced from terminal B,

front contact 2 of relay OR, relay M0 to the other terminal C of the source. In Fig 2, the switch indication relay WK is energized over a stick circuit which may be traced from terminal B, front contact 4 of relay WK, back contacts 2 of relays Si and OFl, relay WK to terminal C. The lever relays Ni and N2 are also energized over their stick circuits, the stick circuit of relay NI extending from terminal B, front contact 8 and winding of relay Ni, left-hand contact l of relay Pi, left-hand or normal contact of switch lever W to terminal C, and that for relay N2 from terminal B, front contact 8 and winding of relay N2, middle contact of signal lever G to terminal C. The lock relay WLI is also energized because the conditions are now assumed to be favorable for the operation of the switch and its circuit may be traced from terminal. B, left-hand contact I of relay TK, left-hand contact 3 of relay MK, front contact 5 of relay N2, relay WLI to terminal C. It is to be understood that relay TK has closed its left-hand contact because the switch section is unoccupied and that indication relay MK occupies a similar position because the signals governing trafiic over the switch have been put to stop and the approach locking associated with these signals has been released. It is clear that since the circuit for relay WLI includes front contact 5 of relay N2, relay WLl will be energized only as long as signal lever G remains in its normal or stop position.

If the operator now reverses switch lever W, the circuit for relay NI will be opened, causing this relay to release to complete a pickup circuit for storing relay Si which may be traced from terminal B, front contact A of relay WLl, back contact I of relay NI, storing relay S-l, knockdown key KD to terminal C. Relay Si, therefore becomes energized and upon picking up completes its stick circuit from terminal B, back contact 1 of relay OFI, front contact 8 and winding of relay Si, key KD to terminal C. Relay P! now reverses, a circuit being closed from terminal B, front contact 4 of relay Sl, front contact 6 of relay WLI, right-hand winding of relay Pl righthand contact of lever W to terminal C. When relay PI closes its right-hand contacts, a pickup circuit for reenergizing relay Ni is completed, providedmaster relay OMR is deenergized, which circuit may be traced from terminal B, back contact 2 of relay OMR, wire I3, back contact I of code-sending relay CSl, front contact I of relay SI, relay Nl, right-hand contact i of relay PI, and the reverse contact of lever W to terminal C. Relay NI, upon picking up, establishes a stick circuit including its front contact 8 and the righthand contacts of relay Pi and lever W, and so will remain energized until lever W is again operated. A pickup circuit for relay CSI is now completed and may be traced from terminal B, front contact 2 of relay Nl, front contact of relay SI, relay CSl to terminal C. When relay NI released, lamp WE became lighted over a circuit from terminal B, back contact I 'of flasher relay FRI, bus wire it, back contact 3 of relay Nl, lamp WE to terminal C, and a circuit was closed from terminal 13, back contact l of relay NI, bus wire I5, back contact 2 of relay FRZ, relay FRI to terminal C so that relay FRI picks up to open the lamp circuit and to close a circuit from terminal B over its front contact 2 to energize relay PR2. When the latter relay picks up, the circuit for relay FRl becomes open and it releases under the control of asymmetric unit l ir and opens the circuit for relay FRZ, which then releases under the control of asymmetric unit I5r' and again closes the circuit for relay FRI. Relays FRI and FR2 thus pick up and release alternately whenever bus wire i5 is energized to supply current intermittently to bus wires l4 and It. Lamp WE will thus flash intermittently as long as relay NI is released, but this will be but momentary in the case described, because relay Si picks up immediately to eifect the re-energization of relay NI. If, however, relay S! should fail to pick up, the flashing indication of lamp WE wouldpersist. In this event the flashing indication may be canceled-by restoring lever W to its original position to complete a circuit from terminal B, back contact l of relay SI, relay NI, left-hand contacts of relay PI and lever W to terminal C, to reenergiz'e relay Ni. However, in the case described, lamp WE will be lighted steadily because when relay Si picks up, the opening of its back contact 12 releases indication relay WK, and as soon as relay Nl picks up, a circuit for lamp WE is closed from terminal B, back contact 4 ofrelay WK,

' back contact 3 of relay OFl, front-contact 3 of relayNl, lamp WE to terminal C. Lamp WE now remains steadily lighted, until an indication code is received to reenergize relay WK, or until lever WI is again operated to'release relay Nl.

If the line circuit is closed and the apparatus is in condition to transmit a code, the energizatlon of relay CSI as described will complete a pickup circuit for relay OMR which may be traced from terminal B, front contact I. of relay OR, back contact 2 of relay OT, back contact I of relay LB, back contacts I and 2 of relay LBP, contacts of relays MC and MO, contact3of relay CT, wire ll, contact 3 of relay CSI, wire 58, relay OMR to terminal C. RelayOlVlRpicks up and completes one branch of its stick circuit which may be traced from terminal B, front contact I of relay OR, back contact 2 of relay OT, back contacts I of LB and LBP, contact 8 and winding of relay OVER to terminal C. When relay OMR picks up, a circuit for relay OT is closed from terminal B, front contact I of relay OMR, back contact l of relay CT, relay OT to terminal C so that relay OT picks up, opening its back contact 4 in the line circuit and releasing relays OR and IR. Relay OMR remains picked up, because'its stick circuit is now closed from terminal B, over front contact 2 of relay OT, back contacts I of relays LB and LBP, contact 8 and winding of relay OMR to terminal C. Relay OR upon releasing completes a circuit from terminal B over its back contact I, relay MC to terminal C so that relaylVlC picks up and completesa circuit from terminal B, front contacts 5 of relays MO and MC, relay L to terminal C. Relay L picks up and closes its front contact 5 to complete a circuit for relay LB, which picks up and the closing of front contact 2 of'relay LB completes a circuit for relay LBP which picks up. The pickup circuit of relay OMR has been opened momentarily, but asymmetric unit 27' in multiple with this relay insures that relay OMR remains picked up until its stick circuit is completed over front contact I of relay LB to again energize relay OMR.

When relay OR released, a circuit was closed momentarily from terminal B, back contact 2 of relay OR, back contact 3 of relay LB, relay OP to terminal C sothat relay OP picks up and a stickcircuit for relay OP was closed when relay LB picked up which may be traced from back contact 2 of relay OR, front contact 3 of relay LB, bus wire I9, contact 8 and winding of relay OP to terminal C. When relay OR released, a circuit was closed from terminal B, back contact I of relay OR, back contact 3 of relay LBP, front contact 3 of relay OMR, lamp CE to terminal C, so that lamp CE becomes lighted. When relay LBP picks up, lamp CE is energized over a circuit from terminal B, front contact 5 of relay LB, front contact 3 of relay LBP, contact 4 of relay OMR, lamp CE to terminal C, so that lamp CE remains steadily lighted for the duration of a control code. Lamp IE is controlled in a similar manner over back contact 3 of relay OMR, and remains steadily lighted for the duration of an indication code. Lamp IE also becomes lighted in the event of a failure of the line circuit, and these lamps serve to inform the operator of any irregularity in the operation of the coding apparatus.

When relay OR released, relay MO became deenergized, but before it releases a circuit is closed from terminal B, back contact 2 of relay OR, front contact 2 of relay MO, register relay SOR to terminal C so that relay SOR picks up to prepare circuits for registering a short code element. The first element of a control code, however, is not a short element and the apparatus remains in the condition just described until relay MO releases, closing a circuit from terminal B, back contacts 2 of relays OR and MO, front contact. 4

of relay L, relay MOR to terminal C, to pick up relay MOR to prepare circuits for registering a medium code element. Relay SOR is now disconnected from the source of energy and releases as soon as its stored inductive energy discharges through asymmetric unit 6?. Relay L is deenergized by the release of relay MO and when it releases the energizing circuit for relay MOR is opened and this relay releases under the control of asymmetric unit Ir. A circuit is now completed over back contact ll of relay L to pick up relay LOR which is controlled by asymmetric unit 81' to prepare circuits for registering a long code element. Thus,'.when the lineremains open, relays SOR, MOR and LOR are operated consecutively to prepare circuits over their contacts I and 2 to register the character of the element when it is terminated. Each line-open code element is term nated by operating relay PT to the right by the closing of a circuit over one of the bus wires 2! or 22 which are connected to relay PT one at a time in turn by the operation of contacts l of relays MO and L. Thus, the first element of a control code is terminated by the closing of a circuit from terminal B, front contact 6 of relay OP, wire 2?, back contacts 5 or" relays L and MO, contact 3 relay OT, right-hand winding of relay PT to terminal C. Relay PT thereupon closes its r ght-hand contact i to complete an obvious circuit for relay CT which picks up, opening the circuit of relay OT, which releases under the control of asymmetric unit I22- to again close its contact 3 in the line.

When the line closes to begin the second element, relay OR picks up, closing its front contact 5 to reenergize relay MO, and relay MO closes its contact 5 to reenergize relay L. The latter relay in turn closes its contact 5 to reenergize relay LB, The circuit for relay LB has been open but a short time and this relay does not release but 'emains picked up for the duration of the code.

When relay OR picked up, the energizing circuits for relays LOR- and OP were opened, but these relays remain picked up for a short time because of the associated asymmetric units Ir, Sr and so that a pickup circuit for relay A is closed momentarily from terminal B, front con tact E era-y OR, front contact 4 of relay LB, bus wire I, front contact I of relay OP, relay 0A to terminal C. Relay 0A picks up, closing its stick circuit from terminal B, front contact 2 of relay OR, front contact 3 of relay LB, wire 3i, front contact 8 and winding of relay 0A to terminal C.

When relay OR picked up, a circuit was closed from terininai B, front contact 2 of relay OR, front contact l of relay LB, front contact 2 of relay MC, relay SCR to terminal C and relay SCR picks up to prepare a circuit for registering a short line closed element. Relay MC is now deenergfzed and when it releases it opens the circuit for relay SCR. to cause this relay to release under the control of asymmetric unit 31' and completes e. :ranch of the circuit just traced over its back front contact 3 of relay L, relay MCR to terminal C, to pick up relay MGR to prepare a circuit registering a medium line-closed eleelay MC also opens the circuit of relay L and lay OR remains energized, relay L will rep aso the end of its time period opening the circgit for relay MCR to cause this relay to release under the control of asymmetric unit 41', re-

bi .nch of the circuit just traced for energizing relay to prepare a circuit for registering a long line-closed element. Thus, when the line 010s 'l, relays SCH, MGR and LCR are .cd consecutively to prepare circuits inclu l ieir contacts l to register the character of the element when it is terminated. Each line closed element is terminated by operating relay ."i to the left by the closing 01' a circuit over one 1 is bus wires 23, M or 25 which are connected relay PT one at a time by the operation of contact i relay MIC and contact 2 of relay L. In the case illustrated the second element is a mcdi n1 element, and relay OR remains energiro: until relax MC releases and closes its back contact to omplcte a circuit from terminal 13,

ont ct 3 of the code-sending relay CS5,

back contact 4 of relay OE, jumper wire wire 2?, back contact 6 of relay OD, jumper wire 28, back contact 5 of relay OC, jumper wire 28, back contact 5 of relay OB, jumper wire 38, front contact of relay 0A, bus wire 24, front contact 2 of relay L, back contact I of relay MC, front contact 2 of relay CT, front contact l of relay LBP, left-hand winding of relay PT, to. terminal C so that when relay MC releases, relay PT operates its contact to the left to deenergize relay CT. Relay CT releases in a short time under the control of asymmetric unit H r and closes its back contact to complete the circuit for relay OT, which picks up to open the line, thereby terminating the element.

When the line opens at the beginning of the third element, and likewise at the beginning of each succeeding odd-numbered element, relay OR releases and rc-cncrgizes relays and L and also completes a connection from terminal B over its back contact 2, front contacts 3 of relays LB and MO, front contact of the register relay SCR, MCR or LCR that is picked up at the time, to energize bus wire 32, E3, or 3 3, depending upon whether the element just terminated was short, medium or long. The register relay remains picked up for a short time because of the asymmetric unit 41' or 51 connected across its windand the stepping relay East energized also remains picked up for a short time because asymmetric unit H1? is now connected to the relay over wire Wires 32, 33 and 34 are connected to contacts 9, 2 and 3 respectively of each of the stepping relays, and a jumper such as wire 36 provides an adjustable connection to one of these three contacts for energizing the next stepping relay of the series. In the case illustrated, the second element of the code is medium, relay OR releasing when relay MCR is picked up, and wire is connected to contact 2 of relay 0A so that vhenrelay OR releases, bus wire 33 is energized momentarily to complete a circuit over contact 2 of relay 0A., wire 38, relay OB to terminal C. Relay OB picks up and completes its stick circuit including its contact 8 and wire 58, this circuit being similar to that described for relay OP, and then relays MCR and 0A release.

The timing and line-open register relays now operate in the same manner as in the case of the first element, but wire 26 now completes a connection over front contact 5 of relay OB to wire 25 so that relay PT will be operated to the right when relay MO releases and the third element will be medium.

When the line closes at the beginning of the fourth element, and likewise at the beginning of the sixth element, relay OR picks up and re energizes relays MO and L and also completes a connection from terminal B over its front contact 2, front contact 4 of relay LB, front contact 3 of relay MC, front contact i of the register relay SOR, MOB or LOR that is picked up at the time to energize wire 3?, 38 or 39. The stepping and register relays last energized remain picked up for a short time-because of asymmetric units i1 and 51', IT or- 87', and jumper wires 65' and provide adjustable connections over contacts 1, 2 or 3 of the stepping relays for energizing the next stepping relay of the series. The third element being medium in the case illustrated, relay OR picks up when relay MOB, is picked up and wire A9 is connected to contact 2 of relay OB to effect the energization of relay OC which thus picks up at the beginning of the fourth element and establishes a stick circuit over wire 3! which is like that of relay OA and then relays MOR and OB release.

In the case illustrated, wire 28 is connected to contact 6 of relay OC and completes a connection to wire 25 when relay 00 picks up to operate relay PT to the left when relay L releases, so that the fourth element is long.

When the line opens at the beginning of the fifth element, relay LCR is energized, and relay OD picks up by reason of the connection of jumper &2 to contact 3 of relay OC, and completes its stick circuit over wire l9 and then relays LCR and 0C release. Relay OD connects wire '2! over its front contact i to wire 29 so that relay PT is operated to the right as soon as relay OD picks up and the fifth element is short.

When the line closes at the beginning of the sixth element, relay SOB is energized, and relay OE picks up by reason of the connection of jumper il to contact I of relay OD, and its contacts 5, 2 and 3 connect wires 32, 33 and 3 to wires 43, M and 45 leading to relays OFl, OF2,.and 0E3, respectively, and completes its stick circuit over wire 3i, and then relays SOR. and ODrelease. Contacts 4, 5 and 6 of relay OE now connect Wires 26, 46 and ll leading to contacts 2 of relays CSl, CS2 and CS3, to wires 23, 24 and 25, respectively. Relay CSl being energized, relay PT will be operated to the left by the closing of the circuit over contact 4 of relayOE as soon as relay OE picks up, so that the sixth element will be short. It is to be noted, however, that two or more of the relays CS may be energized at the same time without interference, because if a circuit is completed over contact 4 of relay OE, relay PT will be operated to the left as soon as relay OE picks up, releasing relay C'Ito open the circuits prepared over contacts 5 and B of relay OE. The codes governed by relays CS2 and CS3 in this instance will be stored, and since the circuit including contact 5 of relay OE similarly takes precedence over the one including contact 8, these codes will be transmitted one at a time in order after the code governed by relay CSi is completed. I

In the code illustrated, therefore, the sixth element is short, and when the line opens to begin the seventh element, relay SCR is energized, and

a circuit is completed over wires 32 and 43 to energize relay OF! which picks up and establishes its stick circuit over wire I9 and then re lays SCR and OE release.

The character of the seventh element of the switch control code is determined by the position of relay PI, and is short or long, depending upon whether the switch is to be operated to normal or reverse. Relay Pl having been operated to the right to reverse the switch, a circuit is completed from terminal B, front contact 5 of relay OMR, wire 43, front contact 6 of relay OF! righthand contact 2 of relay Pi, wire 22, back contacts l of relays L and MO, contact I of relay OT, right-hand winding of relay PT to terminal C to operate relay PT to the right when relay L releases. The circuit for producing a short seventh element to operate the switch to normal differs from the circuit just traced in that it includes the left-hand contact 2 of relay PI, wire 2t, and front contact I of relay MO, andit closes to operate relay PT to the right as soon as relay OFl picks up. When relay OFi picked up, the closing of its front contact 7 established a new holding circuit for relay S! which may be traced from terminal B, left-hand contact l of relay PT, wire 49, front contact 1 of relay OFI, contact 8 and winding of relay SI, key KD to terminal 0. Relay PT is operated to the right to terminate the seventh element before relay OFI releases, and when this circuit is opened, relay SI releases, and opens its contact 5 to release relay CSI,

When relay OR picks up at the end of the seventh element, relay LOR is energized and relays MO and L pick up. The line circuit remains steadily closed, and relays OFI and LOR, MC, L, LB and LBP release in sequence. The opening of front contact I of relay LB causes relay OMR to release, completing a circuit for relay PT which may be traced from terminal B, back contact I of relay OMR, front contact 2 of relay CT, front contact 4 of relay LBP, left-hand winding of relay PT to terminal C, operating relay PT to the left to release relay CT. This completes the transmission of the switch control code and the apparatus of Fig. l is now restored to the condition shown in the drawings. When relay LB releases, relay OP is again connected to back contact 2 of relay OR and the coding unit is in condition to receive a new code. When relay LBP releases, the pickup circuit of relay OMR is again connected to front contact I of relay OR and the apparatus is in condition to transmit another code. The apparatus of Fig. 2 is now also restored to the condition shown in the drawings except that lever W and relay Pl have been operated to the right, relay WK is released. and lamp WE is lighted.

Considering now the station apparatus of Figs. 3 and a, it is to be understood that the slowrelease relays, the register relays and the stepping relays controlled by relay @B have been controlled over circuits similar to those already described and have operated in with the corresponding relays at the office so that relays IP, in, EB, 5C, lD, IE and EF! have each been energized in turn. For convenience in comparthe circuits, the numbered wires in Figs. 3v

and 4 which are a counterpart of corresponding wires in Figs. land 2 are designated by similar references but with a prefix I added, thus for example, relay lFi is energized over a circuit including wire I53 when relay-OF! is energized over wire 63. Relay IMR at the station, how- 'ever, is not. energized when receiving and the associated transmitter relays iT, CT and PT at the station have not been operated.

The seventh element of each. code is registered by circuits closed only when the coding unit functions as a receiver. Thus when relay IR. picks up at the end of a control code, relay iMR is not energized and a connection is established from terminal B, front contact 2 of relay IR. front contact l of relay LB. front contact 3 of relay MC, back contact 3 of relay IMR, front contact 2 of relay SOR, MOB, or LOR to wire iiifl. 655 or l52. I

The seventh element of the switch control code described being long, relay LOB. at the station is energized when relay l3. picks up at the end of the code and the register circuit is completed from wire I52. over front contact 3 of relay lFl, right-hand winding of relay WS to terminal C,

so that relay WS will be operated to close its contacts to the right. Assuming that'track relay TR for the switch section is energized, the signals governing traflic over the switch are at stop, and that the approach locking relays LMR and RMR controlled by these signals are energized, a circuit will be completed from terminal 13, right-hand contact 2 of relay 'WS, wire 53,

patent hereinbefore referred to.

front contacts 2 of relays LMR, RMR and TR, polar switch operating relay WR, front contacts i of relays TR, LMR and RMR, wire 54%, righthand contact I of relay WS to terminal C so that relay WR will close its right-hand contacts to complete circuits for energizing the motor of the switch machine to operate the track switch to reverse. When the seventh element of the switch control code is short, relay WS is operated to the left by a similar circuit including front contact 2 of relay SOR, wire I and contact I of relay IFI, and relay WR is operated to the left to restore the switch to normal.

Each switch control code also operates the storage relay IS to initiate the transmission of an indication code. When relay IFI picks up, a circuit is closed from terminal B, back contact 2 of relay EMR, wire H3, front contact 5 of relay IFI, relay IS to terminal C. Relay lS picks up, closing its stick circuit from terminal B, back contact I of relay ICS, front contact 8 and winding of relay IS to terminal C. Relay IS remains energized, storing the code if the line is not available for transmission.

The switch machine for switch ISM is provided with the customary circuit controller contacts indicated by the reference SM in Fig. 4 for controlling the polar switch indication relay KR. These contacts operate to cause relay KR to become deenergized as soon as relay WR is operated to a position out of correspondence with that of the switch or when the switch is unlocked, and to become energized in the reverse direction when the switch completes its operation and is locked reverse, as illustrated in the Kenimerer When relay 5S becomes energized, the polar relay WV is operated to a position corresponding to the condition of relay KR. Thus, when relay KR releases due to the reversal of contact 3 of relay WR, relay IS having been energized as above-described. a circuit is closed from terminal B, back contact I of relay KR, wire 55, front contact I of relay IS, right-hand winding of relay WV to terminal C. Relay WV closes its right-hand contact 5 to cause the seventh element of the indication code to he medium to indicate the unlocked condition of the switch.

The tiated comes would switch indication code is also at times iniautomatically, in the event relay KR bereleased due to conditions in the field, as be the case, for example, if the switch points become displaced so that the circuit controller contacts SM become open. In this case relay is is energized in the following manner: When relay KR releases, a circuit is closed from terminal B, back contact I of relay KR, wire 55, left-hand contact 2 of relay WV, starting relay iST to terminal C. Relay IST picks up and closes a circuit from terminal B over its front contact 2, relay IS to terminal C. Relay IS then picks up, closing its stick circuit and completing the circuit to cause relay WV to close its righthand contacts as already described, relay iST ragain releasing when the left-hand contact 2 of relay WV opens. A switch indication code is also initiated when relay KR picks up, as for example, when the switch completes itsmoveznent to a position corresponding to that of relay WR, the circuit for relay l ST in this case including front contact I of relay KR, wire 56 and the right-t contact 2 of relay WV, the latter relay being operated to the left to release relay IST soon as relay IS picks up to close its contact 6. In this code, the character of the seventh element is determined by the position of contact 2 of relay KR and is short if the switch is locked normal and long when it is locked reverse.

The switch indication code includes an indication of the condition of the approach section, and is initiated automatically whenever relay AR picks up or releases. When relay AR releases, a circuit is closed from terminal B, back contact i of relay AR, wire 51, left-hand contact 2 of relay AV, relay EST to terminal C. Relays IST and IS pick up, and then a branch of the circuit just traced is completed from wire 5?, back contact 5 of relay ICS, front contact 4 of relay iS, righthand winding of relay AV to terminal C, so that relay AV is operated to the right to release relay EST. When relay AR picks up, relays EST and IS are operated as above described and then relay AV is restored to the left, as shown in the drawing, by the closing of a similar circuit from termi nal B, front contact I of relay AR, wire 58, back contact of relay ICS, front contact 5 of relay IS, left-hand winding of relay AV to terminal C. The position of contact I of relay AV determines the character of the first element of a switch indication code, this element being short when contact 5 of relay AV is closed to the left and medium when it is closed to the right. Contacts 3 and 5 of relay ICS are included in the circuits of relay AV to insure that this relay will not respond when relay AR changes its position during a code in order to delay the release of relay IST under these circumstances until the code then in progress is completed and the apparatus is in condition to transmit a new code.

Considering now the transmission of the switch indication code initiated by picking up relay IS, if relay ISC has released relay IS is held energized over 'oack contact I of relay ICS and if the line is available, a pickup circuit for relay ICS is closed from terminal B, front contact I of relay IR, back contact 2 of relay IT, back contact l of relay LB, back contacts I and 2 of relay LBP, contacts 4 of relays MC and M0, contact 3 of relay CT, wire I I1, front contact I of relay IS, back contact I of relay IST, relay ICS to terminal C. Relay ICS picks up, establishing a. new holding circuit for relay IS which may be traced from terminal B, back contact 3 of relay LBP (Fig. 3), back contact 2 of relay LB, wire 59, back contact I of relay IFl, front contact I of relay ICS, front contact 8 and winding of relay IS to terminal C. Relay ICS when energized closes a pickup circuit for relay I MR, which is the same as the circuit just traced for relay I CS from terminal B to wire H1, and then extends over front contact I of relay IS, back contact I of relay IST front contact 2 of relay IS, front contact 4 of relay ICS, wire H8, relay IMR to terminal C. Relay IMR picks up, closing its stick contact 8 and establishing a holding circuit which is similar to that for the corresponding relay OMR of Fig. 1. Relay IMR closes its front contact I to operate relay IT to initiate the code as already described in connection with Fig. 1. When the station relay LB picks up, the holding circuit for relay IS becomes energized by a connection from. terminal B over front contact 2 of relay LB to wire 59 and thence as already described through relay IS to terminal C. The pickup circuit for relay ICS becomes opened as the various relays controlling this circuit are operated, but relay ICS is held energized over a stick circuit which extends from terminal B over front contact I of relay IR or front contact 2 of relay IT, front contactl" of. relay LBQfront ccntactt of relay already described. Assuming theapproach section to -.be.unoccupied so vthat relay ARis energized, thefirst element will be short and will be determined by a circuit which may. betraced from terminal B, front contact 2 of relay lP,'

wire 60, front contactfi of relay l-CS, left-hand contact I of re1ay AV, wire we, front contacts I: of relay MO and IT, right-hand winding of relay PT to terminal C, so that relay PT will be operated to the right as soon as relay IP transmitter control circuits forv these elements may be energized by connecting terminal B di-- picks up. "If on the other hand the code being described i s-transmitted when AR is 'deenergized, contact 1 l oi-relay AV will be closedto the right and the circuitin this case will be completedover wires til and lZl and relay PT, will be operated to the right when relay MO releases to close its back contact i, so that in this case the; first element Will be medium. After completing the first element, the coding apparatus of Fig. 3 continues to transmit the several selecting elements of-the code in the manner already described in connection with Fig. 1. Cer tain of thecircuits are arranged differently however in order to adapt the apparatus for use in installations havinga plurality of stations, and these diiferences will now be pointed out. Some of the code elements will, in general, be identical in all codes transmitted from a station, .and the rectly to contact 6, 5 or 6 of the stepping relays,- in place .of a jumper connection to a contact '2 of a relay CS, as illustrated for examplefby the connection to contacts 5 of relays IA and [Band to contact 6 of relay lC. Furthermore, the pickup circuit of relay EA is so arranged that the sta tion receiver will not respond to the first element of an indication code transmitted by another station. This pickup circuit has two branches, one of which includes'iront contact I of relay IP and a front contact I of register relay LOR and serves to cause relay IA to become energized when receiving a control code, because the first element of each control code'is long.' The other branchincludes front contacts 3,0f relays IMR tion "is sending an indication code. IF! picks up at the beginning of the seventh'eleand, IP', and, serves to cause relay lAto become energized when the station is sending anfindication code, ,sincein this case relay IMR. is en-' ergized. Both branches will be open and relay IA will not become energized when another sta- When relay ment it opens its back contact l'to effect the release of relay IS, and the latter relay then'opens its front contacts to cause relay ICS .torelease'. The circuit for generating the seventh element, which in the case illustrated is medium and refiects the unlocked condition of the switch,-be

comes closed whenrelay MO releases and may be traced from terminal B, front contact fi ofrelay lFl', right-hand contact l of relay WV, wire I21;

and'thence over contacts I of relays L, MO and IT andright-hand winding ofrelay PT to terminal C. When relay lR picks up at the end of the code, theline remains steadily closed,'relay MO picks up, and relays lFl and MOR; MC, L,

MR and LBP'release insequence in a mannerqsimilar to'that already described.

When the-switch completes its operation, indication relay KR becomes-energized in the reversedirection, closing itsright-hand polar contactwii and 'completing a startingcircuit sothat relays 1ST, IS and ICS will again pick up, as already described, to initiate a second code. In this code, the-seventh element will be long and will be determined by a circuit which may be traced fronrterminal' B, front contactfi of relay position of the device which initiated the code and then release toenergize the corresponding code sending relay CS. .The pick up and stick circuits .for each-relay CS of aseries of storage units-except that of the first unit of the series are arrangedlina series hunting circuit including back'ccntacts i and i of relay S and CS of each preceding storage unit and wires 1 I7 and H8 respectively, so. that relay'CS of but one storage unit can be. energized at a time. Furthermore, at the begin'ningof the code, the holding circuit of the energized storing relay S is transferred to wire 59; and in the event of a failure becomes opened due to the consecutive release of the station relays LB and LBP Which'control the connection of terminal B to wire 59. Since the device which initiated the code and its relay V now occupy corresponding positions, the starting relay ST'remains deenergized until another change in the position of' one of the device's controlling the storage unit takes place. Each storage unit is thus given but one opportunity to initiate a given code.

Considering now theoperation of the ofiice coding unit ofFig. 1,: in receiving a switch indication Jccde, although most-of the operations are the same as when transmitting, since relay OMR.

is:deenergized, certain operations will take place which donot occur when the coding-unit operates as a trans'mitter and thesewill now be explained. Thug-when relay OR picks upat the end ofan indication. code, relayOlViR, is not energized and a' 'connecti'onis established from terminal B, front contact 2 i relay OR, contact lof relay LB, contact-3 ofrelay MC, backcontact 3' ofrelay OMR' and'contactl'fi of a register relay to "wire ll, 5| or 52.- If the first element of the indication code is short, relay .OR will pick up while relay SOR energized and "complete a register circuit from Wire 56, over front contact 30f relay OP, relay TC to'terminal C. If the first element is amedium element, it is terrninated while relayMOR is picked up, and a---siinilar circuit is completed over 54 and contact-'4 of relay OPto pick up relay TOL It is evide'nt therefore, that either relay TC' 'orflrelay T0 is picked up depending upon whether the first element is short or medium.

Relay TC or T0 when picked up will complete its stick'circuit-which may betraced from" terminal B,-front contact 5 of relay LB,,front.contact"4 and windingofthe relay. to terminal'C'sb that'it will remain picked up. untill'relay LBv releases at the end-ofthe code. i

Assuming thatthe code; is the. first; of the two switch indication codes described and reflects the unlocked condition of the switch, when relay OFI picks up, its back contact 2 in the stick circuit of relay WK opens to release relay WK if energized. In case this code is initiated automatically, therefore, relay WK is released to light lamp WE to inform the operator that the switch has been unlocked or displaced, contact I of relay WK opening to prevent the energization of relay CS2 to send acode to clear a signal governing the movement of traffic over the switch. However, in the case described, relay WK was released when the control code was transmitted to operate the switch and therefore the first indication code effects no change in the office indication apparatus.

When the indication code is received having a long seventh element indicating that the switch is locked reverse, a register circuit is completed at the end of the code from terminal B to wire 52, thence over right-hand contact 3 of relay PI, front contact 2 of .relay OFi, relay WK to terminal C, so that relay WK will pick up, extinguishing lamp WE and closing its contact I to prepare a circuit for relay CS2. When relay OFI releases, the stick circuit of relay WK will again become closed so that relay WK will remain energized to cause lamp WE to remain dark. If the switch is operated to normal so that contact 3 of relay PI is closed to the left as shown in the drawing, the seventh element. of the indication code must be short in order to pick up relay WK, indicating that the switch is locked normal, the pickup circuit for relay WK being completed in this case from terminal B, over wire 50 and the left-hand contact of relay PI. It will be apparent that relay WK only becomes energized when relay PI at the oiiice and relay KR at the station occupy corresponding positions.

When relay OFI picked up at the beginning of the seventh element of the switch indication code, the ofiice indication relay AK was operated to a position corresponding to that of relay AV at the station. Thus assuming that relay TC has been energized by a code indicating that the approach section is clear, when relay OFI picks up a circuit is closed from terminal B, front contact I of relay TC, wire 62, front contact 4 of relay OFI, left-hand winding of relay AK to terminal C. This will be without effect if the contacts of relay AK are already closed to the left, but if these contacts are closed to the right they will be returned to the left, contact I of relay AK opening to extinguish lamp AE. Contact 2 of relay AK is included in a circuit which may be traced from terminal B, contacts 2 of relays TK and AK, wire 63, contact 4 and winding of the bell relay XR to terminal C. This circuit opens momentarily when contact 2 moves from right to left, but this is without effect because relay XR is at that time energized by a pickup circuit from terminal B, back contact I of relay TO, relay XR to terminal C.

If now a code is received indicating that the approach section is occupied, relay TO becomes energized instead of relay TC, relay AK will be operated to the right by the closing of a circuit from terminal B, front contact I of relay TO, wire 64, contact 5 of relay OFI, right-hand winding of relay AK to terminal C. Lamp AE will become lighted, and the momentary opening of contact 2 of relay AK will cause relay XR to release and close its back contact I, thereby causing a single stroke operation of bell KB. This occurs near the end of the code, and shortly afterward relay LB releases, restoring relays TO and XR and bell XB to their normal condition. Repetition of this code obviously is without efiect,

the contacts of relay AK remaining to the right,

the bell sounding but once irrespective of the number of consecutive similar codes received.

We will now explain the operation of the storage units for governing the signals. We will assume that the operator has reversed lever W as described to send a code to reverse the switch and that he at once moves lever G to the right for the purpose of clearing arm b of signal R2. Relay N2 becomes released, deenergizing relay WLI to lock relay PI against operation. If lever W is moved again, before the switch control code is completed, relay N I will release but relay CSI will be held energized until relay SI releases at the end of the code by a circuit from terminal B, back contact 4 of relay WLI, contact 4 ofv relay CSI, contact 5 of relay SI, relay CSI to terminal C, so that the transmission of the switch code already initiated can not be interfered with. When relay N2 releases, if the left-hand contacts of relay MK are closed, a circuit is completed from terminal B, contact I of relay MK, righthand winding of relay P2 and right-hand contact of lever G to terminal C to operate relay P2 to the right. As soon as the transmission of the switch control code above described is completed, relay OMR releases, and a circuit is closed from terminal B, back contact 2 of relay OMR, wire I3, back contacts I of relays H2 and N2, storing relay S2, key KD to terminal C, so that relay S2 picks up, completing a circuit from terminal B, back contact 4 of relay CS2, front contact 4 of relay'SZ, relay H2, right-hand contact I of relay P2, right-hand contact of lever G to terminal C. Relay H2 picks up and closes its stick circuit extending from terminal B, front contact 8 and winding of relay H2, the right-hand contacts of relay P2 and lever G to terminal C. Terminal B is now connected over back contact 2 of relay CS2, and front contact 6 of relay S2 to bus wire I5,to actuate the flasher relays FRI and FRZ and lamp HE becomes energized intermittently over a circuit from terminal B, front contacts I of relays FL! and FL2, bus wire I6, back contact I of relay CS2, front contact 2 of relay S2, lamp HE to terminal C. As soon as a code is received, indicating that the switch has completed its operation to a position corresponding to that of relay PI so that relay WK picks up, a circuit is closed from terminal B, front contact I of relay WK, contact 5 of relay NI, contact 2 of relay H2, contact 5 of relay S2, relay CS2 to terminal C. Relay CS2, upon becoming energized, opens its back contact I in the circuit for lamp HE and its contact 2 in the circuit for actuating the flasher relays so that lamp I-IE remains dark and the operation of the flasher relays is discontinued. Relay CS2 also closes its front contacts 3 and 2 to initiate a control code which is transmitted in the manner hereinbefore described in connection with relay CSI, except that in this instance the character of the sixth element of the code is determined by a circuit completed over wire 46, leading to contact 5 of relay OE so that the sixth element of the code will be a medium element, and relay OFZ will become energized instead of relay OFI. The character of the seventh element of the code is determined in this case by a circuit which may be traced from terminal B, front contact 5 of relay OMR, wire 48, front contact 6 of relay OFZ, front contact I of the code.

relaysPZ' and WM. its left-hand position only by the receipt of a,

relay SZQback contact 3 of relay N2, right-hand polar contact 2 of relay P2, wire 22, back contacts I of relays L and MO, contact l of relay OT, righthand winding of relay PT to terminal C, and will therefore be terminated when relay-L releases and will be a long element. If lever G and relay P2 had been operated to the left, the seventh elementof the code would have been determined by a similar circuit over the left-hand contact 2 of relay P2 and wire 20, and so would have been a short element. 9

When relay OF2 picks up, the connection from terminal B over its back contact l for energizing the stick circuit of. relay S2 is opened, and this circuit becomes energized by a connection from terminal B, left-hand contact l of relay PT, wire 49, and front contact I of relay OFZ, so that relay S2 releases when relay 1 T is operated to the right to terminate the seventh element of MK, key KD to terminal so that relay MK is operated to the right to open the circuits for Relay MK is returned to code indicating that the signal are at stop and the approach locking is released, and until such code is received, relay Pi is locked to prevent the transmission of a switch control code, and relay P2 is locked to prevent the transmission of a code for clearing a signal for the direction of trafiic opposite to that which has been established.

The control code for clearing signal R2 causes the station coding unit of Fig. .3 to operate to receive the code in a manner similar to that already described except that in this case relay [F2 will pick up instead of relay lFl, and the seventh element being long, at the end of the code a register circuit is completedfrom terminal B,

, LH of the Kemmerer patent, hereinbefore referred to.' In any event, it is to be understood that arm 13 of signal R2, selected in accordance with the position of. the track switch, will clear if trafiic conditions are favorable, so that the corresponding indication relay RGP will become released and then the approach locking relay RMR will become released to lock the switch against operation. .These relays govern the repeating relay MP overa circuit which may be raced from terminal B, contacts 3 of relays LHS and RHS, wire 67, contacts 3 of relays LMR and RIVLR relay MP to terminal C. Relay MP releases when a signal clear code is received and then completes a circuit from terminal B, back contact i of relay MP, wire 68, resistor 69, right-hand winding. of relay MV to terminal C, operating relay MV to the right to prep-are a' circuit for initiatinga code when relay MP again picks up.

It is toJbe understood that no indication code will be initiated following the receipt of a signal When relay S2 releases a circuit is clear control code in the event thesignals remain at stop.

When signal R2 clears,re1ay RGP releases, and a circuit is closed from terminal B, back contact I of relay'RGP, wire N1, left-hand contact 2 of relay GV, storing relay EST to terminal C. Relay 2ST upon picking up, completes a circuit for relay 23 in a manner similar to that already described in connection with relay IS,

relay 2S closing its contact l to operate relay GV to the right to open the startingcircuit to release relay 2ST. Relay ZSremains energized to store the code until the line becomes available for transmissionand then the code sending relay 2CS becomes energized, initiating the transmission of the code as already described, except that in this case the character of the-first element is determined by a circuit which includes contact '6 of relay ZCS and contact I of relay TV and Wire I20 or 52H, for causingthe first element to be short or medium to indicate the clear or occupied condition, respectively :of the track section lT. The character of the seventh element is determined by circuits which include front contact 6 of relay IE2 and contacts I of relays GV and MV. In the case illustrated, relay GV has been operated to the right, completing a circuit from terminal B, contact 6 of relay iFZ, right-hand contact l of relay GV, to wire I22, so that the seventh element of the code willbe long.

When the signal clear indication code is received at the oilice, relay OF2 will be operated, then wire 52 will be energized to complete a circuit including contact 3 of relay OF'Z and the left-hand winding of relay I-IK to terminal C. Relay HK will be operated to the left, {completing a circuit from terminal B, contact i of relay HK, back contact 2 of relay S2, lamp HE to terminal C so that HE becomes steadily lighted to indicate that the signal has been cleared. Relay WLl is now deenergized and relays Pi and P2 are locked against operation.

A code may now be transmitted to put the signal to stop, by moving lever-G to its midposition, or the signal clear code may be repeated, by moving lever G away from and back to its right-hand position to effect the momen- 'tary release of relay H2, but no other codes can be transmitted as long as the contacts of relay MK are open. Forv example, if lever W is restored to normal, relay N! will release to cause lamp WE to display a flashing indication, or if lever G is reversed, relay H2 will release and relay S2 Will pick up to cause lamp HE to display a flashing indication.

Assuming that the signal is to be put to stop, lever G is restored to its mid-position, and then relay H2 releases, closing its back contact I to again energize relay S2. When relay S2 picks up, a circuit is closed from terminal B, back contact 5 of relay CS2, contact 3 of relay S2, relay N2 and the middle contact of lever G to terminal C so that relay N2 picks up to again establish its stick circuit, and to close ,a circuit from terminal B, contact 2 of relay N2, contact 5 of relay S2, relay CS2 to terminal C so that relay In this code the circuit for 2 of relay S2 while the code is being transmitted. When the signal stop code is received at the station, the medium seventh element will be registered by the closing of a circuit over wire II, front contact 2 of relay IF2, right-hand winding of relay LHS, left-hand winding of relay RHS to terminal C, so that these relays will be restored to the positions shown in the drawings. Arm 1) of signal R2 will therefore be restored to stop and relay RGP will again be energized, but if the signal is put to stop when the approach looking is effective, relays RMR and MP will remain deenergized. In this case an indication code will be initiated when relay RGP picks up completing a circuit for relay 2ST over wire H which is similar to that over wire Ill already described, and relay GV will be operated to the left by the closing of the circuit over contact 6 of relay 2S. When relay IF2 is energized, a circuit will be completed from. terminal B, contact 6 of relay IF2, left-hand contact I of relay GV, righ hand contact I of relay MV to wire I2I to operate relay PT to the right when relay MO releases, so that the seventh element of the indication code will be medium. 1

When this code is received at the oifice, wire 5I will be energized when relay OF2 is picked up, completing a register circuit over its contact 2 and the right-hand winding of relay HK to terminal C, operating relay HK to the right to extinguish lamp HE.

When the approach looking at the station is released by the energization of relay RMR, relay MP will become energized, completing a circuit from terminal B, wire 72, right-hand contact 2 of relay MV, relay 2ST to terminal C to initiate an indication code and to restore relay MIV to the left, as shown in the drawing by the closing of a circuit over contact 5 of relay 2S. When relay IE2 is energized, a circuit will be completed from, terminal B, contact 6 of relay IFZ, left-hand contacts I of relays GV and MV to wire I20, to that the seventh element of the code will be short.

When this code is received at the ofiice, wire 50 will be energized when relay OF2 is picked up, completing a register circuit over its contact I, left-hand winding of relay MK, right-hand winding of relay I-IK to terminal C, operating relay MK to the left, so that relays PI and P2 will again respond to the operation of their respective control levers. It is apparent, therefore, that the operator may send a code to put the signal to stop and immediately thereafter may operate the switch lever W, but the switch code will be stored and will be transmitted when an indication of the release of the approach locking is received.

The character of the first element of each signal indication code is determined by circuits including contact 6 of relay 20S and contact I of relay TV, which function in the same manner as in the case of the corresponding circuits controlled by relays I05 and AV already described, and a code is initiated whenever track relay TR picks up or releases. If relay TR releases, its repeater relay TP will be released completing a circuit from terminal B, over its back contact 4, wire I3, contact 3 of relay TV, right-hand winding of relay TS to terminal C, operating relay TS to the right to close a circuit over contacts 2 of relays TV and TS to pick up relay 2ST. Relay 28 then picks up, closing a circuit from terminal B, back contact 2 of relay ZCS, front contact 4 of relay 2S, right-hand contact I of relay TS, righthand winding of relay TV to terminal C, operating relay TV to the right to release relay 2ST to initiate the code. As in the case of relay AV, the circuit for relay TV includes a back contact of relay 20S and therefore relay TV does not respond to a change in conditions while the code is being transmitted. When relays TR and TP again pick up, a circuit is closed from terminal B cover front contacts 4 of these relays, wire I4, contact 5 of relay TV, back contact 3 of relay 2S, left-hand winding of relay TS to terminal C, restoring relay TS to the left as shown in the drawing to again pick up relays 2ST and 2S to restore relay TV to the left, as shown in the drawing. Unless relay 28 becomes released due to a failure of the apparatus, it will remain energized until the track-occupied code is transmitted, and if relay TR picks up, the track-clear code will not be transmitted until after relay 2S releases to close its back contact 3.

The operation of the track indication relay TK is similar to that of relay AK already described, as will be apparent from the drawings.

We will now assume that a signal has been cleared and that a train accepts the signal and enters section IDT. Relay TR will release, deenergizing the slow-release relay TP. Before relay TP releases, a circuit is closed momentarily from terminal B, front contact 4 of relay TP, back contact 4 of relay TR, back contact 2 of relay CHS, wire 15, back contact 2 of relay IF2, right-hand winding of relay LHS, left-hand winding of relay RHS to terminal C, restoring these relays to the positions shown in the drawings, so that the signals will remain at stop until the signal control relays are gain operated by a signal clear code.

We will now assume that the operator, in order to facilitate the movement of a fleet of trains moving in the same direction, operates lever G to clear the signal and then operates key NSK. As indicated in the drawing, key NSK is provided with a spring actuated latch I6, which is held away from the key by a cam 11 on the shaft of lever G, when lever G is in its mid-position. When lever G is moved to the left or right to clear the signal and key NSK is operated, latch l6 becomes effective to hold the contact of key NSK. closed against the action of its restoring spring. Although shown at one side for clearness, key NSK is preferably located behind lever G so that it can be operated only when lever G has been moved to the left or right, and it is evident that the contact of key NSK will open automatically when lever G is restored to its mid-position. Key NSK having been operated, when each train enters section IDT, relays LHS and RHS will be restored as described, and a code indicating the condition of the signals and of the track section will be transmitted, and a second code will follow as soon as the train leaves section IDT. At the end of this latter code, relay TC will be energized and relay TK will be operated to the left to extinguish lamp TE, and relay SOR or MOR will be energized so that a circuit will be closed from terminal B, front contact 2 of relay OR, contact 4 of relay LB, contact 3 of relay MC, back contact 3 of relay OMR, asymmetric unit 537*, contact 3 of relay SOR or MOR, contact 2 of relay TC, wire I8, contact 9 of relay OFZ, key NSK, relay S2, key KD to terminal C. The unit I31" prevents improper operation of connected circuits such as might occur if current were permitted to flow in the reverse direction in this circuit. It follows, therefore, that when the train 76 leaves section IDT, relays2 will become energized and will therefore automatically initiate a signal clear code to again position relays RHS or LHS, so asto cause the signal to clear fora following train as soon as the first train has moved beyond the control limits of the signal,

We will now explain the operation of the apparatus employing the control code associated with relays jOFt and iF3. It will be assumed that the operator has sent a code toclear arm a or b of signalRZ, butthatthe block is occupied so that the signal isprevented from clearing, and that he desires to then clear the low speed arm 0 to permit a following train to enter the occupied block. The operator then closes key CO,-and if lever G is in its left-hand or right-hand position so that relay H2 is energized, a'circuit is closed from terminal B, back con-tact Z of relay LB, wire 19, contact 4 of relay H2, relay CS3, key CO to terminal C. Relay CS3 picks up, closing its contact 3. to initiate the code and its contact 2 to connect terminal B to wire 4'! which leads to contact 6 of relay OE and completes circuits for determining the character of the code so that relays OF? and IFS will be picked up at the beginning of the seventh element, by the closing of circuits over wires 55 and M5, respectively. The character of the seventh element is determined by a connection from terminal B over wire 48, front contact 2 of relay OF3 to wire 22 and is therefore a long element. Key CO is a spring return key and is held closed by the operator until this element is transmitted, as indicated by the momentary lighting of lamp HE and then may be released. Relay CS3 is held energized during transmission by the closing of its stick circuit from terminal B, contact 8 of relay CS3, contact lof relay H2, relay CS3, key CO to terminal C. Lamp HE is momentarily lighted to indicate when key CO may be released by the closing of a relay CHS to terminal C. If relay LHS or RHS has been reversed to close its contact l, relay CHS will pick up, completing a connection from terminal B,- contact A of relay CHS to wire Bl so that relay OHS will remainenergized until the signal is put to stop manually, the circuit over wire '55 for restoring the signal control relays whenrelay' TR releases now being open at back contact 2 of relay CHS. Contact l of relay CHS may be included in a circuit for controlling the lowspeed arm 0 of the signal, as in the Kemmerer patent hereinbefore referred to, so that this signal will clear when relay CHS is energized. I

We will now explain how our apparatus is arranged when used to control a plurality of switches and signals. Since the stepping relays function in a like manner on each step of the code, circuits such as those illustrating the selection of the final stepping relay F may be en ployed to select one or more of the preceding stepping relays of the series. Thus, for example two more relays OEmay be: added to Fig. 1, with their-jumper wires' ii and 2? connected to contacts 2 and 5 and to contacts 3 and 6, respectively, of relay OD, and then relay OD will control three relays .OE just as relay OE now, controls three relays OF; Fig. 1, together with three copies of Fig. 2, will then form a complete drawing of the office circuits'for the control of nine station devices. It will be clear that in this arrangement the numbered bus wires of Fig. l are to be connected in multiple to the corresponding terminals of each Fig. 2, butthat there will be three groups of wires #3, 44, 45, and also three groups of wires '26, 46, and 41, and for each Fig. 2, and the bell circuit includingwire 63 will extend in series through the contacts 2 of all relays AK and TK.

- include two additionalrelays E with jumper wires Ml and till" connected to contacts 2 and .5, andto contacts 3 and 6, respectively, of relay 5D, and then Fig.. 3 together with three copies of Fig. 4 will form a complete drawing of the. station circuits for the control of nine devices at a station. The numbered bus wires of Fig." 3 are to be connected in multiple to the corresponding terminals of. each Fig. 4, but there will be three groups of wires M3, M4, M5, and also three groups of wires 1126, I46 and ldl, one for each Fig. 2, and the circuits including wires Ill and H8 will extend in series through the back contacts of all. relays S and .CS, respectively. Furthermore, the arrangement of storage units shown in Figs. 2 and 4 may be varied according to the requirements of the system and relays OE and IE may control three switches or three signals or govern the indication of six track section's. By a similar process the apparatus may be further extended so that ultimately allthe different codes are employed, the circuits then being arranged so that each stepping relay controls three-relays,"

thus relay 0A will control three relays'OB, and t ere will be nine relays OC, twenty-seven relays OD, eighty-one relays'OE and two hundred fortythree relays OF.

' Our apparatus is so'arranged that the different codes may be transmitted over the same line circuit without interference. It has already been pointed out that no interference between control codes occurs if for'example, relays CSI, CS2 and CS3 are energized at the same time, because if the circuit including contact '4 of relay CE is closed it terminates the element and the circuits including contacts 5 and 6 of relay OE are rendered ineife'ctive', the codes corresponding to the other two relays Csbeing transmitted one at atime thereafter. The connections will be similarly arranged in the case of any code element when two or three of the possible characters are employed, and in each case, a short element takes precedence over a medium element and the latter takes precedence'over a long element, so that no interference can occur between the different conmitted from the same station, because the cirup. at the same time, relay OT will remain up to" generate a long first element after relays T re-' lease, but the line relays R will fail to pick up because the line isheld open by relay OT. The

holding circuit for relay MR at each station If relay OT at the including back contact 2 of relay T and front contact 1 of relay R will therefore be opened and relay MR at each station will release, thereby conditioning the station coding units to receive the control codes from the office. A somewhat different result will occur in the event two stations start the transmission of indication codes at the same time. If the code initiated by one station has a short first element and that initiated by the other has a medium first element, the latter code will take precedence, relay MR at the one station releasing as above described but in this case opening the pickup circuit for the stepping relay A which includes front contacts 3 of the station relays MR and P to interrupt the operation of the stepping relays at that station. In the event one or more successive elements of indication codes initiated simultaneously by different stations are identical, the relays T will operate in unison until a point is reached where an element of one code is of different length from the corresponding element of the others. If this is a line-open element, a medium element takes precedence over a short element and a long element takes precedence over either, as in the case of a first element. If it is a lineclosed element, the reverse is true, a medium element taking precedence over a long element, and a short element taking precedence over a medium or a long element. Thus when a relay T picks up to terminate a line-closed element, the release of relay R at each station at which relay T has not picked up opens the holding circuit for relay MR at such station. It is clear, therefore, that in each case of simultaneous initiation of different codes but one relay MR will remain energized, and since the jumper connections to contacts I, 2, 3 of the stepping relays are diiferently arranged at the different stations and no station can register an element which is not part of its code, but one pair of relays OF and F will be operated. It follows, therefore, that our apparatus possesses such flexibility that may be readily adapted to a wide variety of different conditions, and that each tmits may-be arranged precisely in accordance with the needs of the system without including any idle apparatus, and that the apparatus will operate in an efficient and reliable manner because of the simplicity of the line circuit and of the various safeguards against improper operation hereinbefore described.

In the foregoing, our apparatus has been described with reference to an isolated switch and group of signals, but frequently a number of switches may be so located that one signal is interlocked with others and controls a plurality of routes, and each route may be determined by the positions of a number of different switches. Our apparatus is particularly adapted to control such interlocked switches and signals, and when so employed the circuits for relays WL! and CS2 by means of which the control levers are electrically interlocked may be modified or extended to include contacts governed by other related levers or devices. In explaining this feature of our invention reference will be made to Figs. 5 to 9, inclusive. Fig. 5 is a track plan typical of interlockings in general, comprising two switch sections 3DT and 5DT connected by a crossover, the two sections being independent so that parallel train movements may be made when the crossover switches 3SW and 3A--SW are normal, but forming part of the same routes when the crossover switches are reversed. It is to be un erst od that the apparatus of Fig. 5 is arranged in two groups, each similar to that hereinbefore described, one including sections 5DT and 5AT, switch 5SW and signals 6L and SR, the other including sections 3DT and 3AT, switch 3SW and signals 4L and 4R, while switch 3A--SW is operated in unison with switch 3SW and is controlled by the same relay WS. It is further to be under stood that the coding unit for controlling these groups is governed by the line relay bearing the reference 3R in Fig. 10, that this unit is arranged with two relays E in the manner hereinbefore described, including one for each group, and that the circuits for each group are similar to those of Figs. 2 and 4 except that the circuits corresponding to those of relays WLI and CS2 in Fig. 2 are arranged as illustrated in Figs. 6 and '7, each of the relays WL and CS for ready identification, being designated by the number of the signal or switch with which it is associated.

The various contacts in Figs. 6 and 7 are for simplicity shown apart from the relays which operate them, but each contact bears a number identifying the contact as in Fig. 2, and above this number is a reference identifying the relay which operates it, comprising a letter or letter combination identical with that of the corresponding relay of Fig. 2 followed by a number identifying the switch or signal with which the relay is associated. Thus, in Fig. 6, code sending relay CS6 for governing signals R6 and L6 has a circuit which may be traced from terminal B, contact 2 of relay N6, contact 5 of relay S6, relay CS6 to terminal C which may be closed to initiate a code to put signals L6 and R6 to stop, and relay CS4 has a similar circuit which may be closed to initiate another code to put signals L4 and R4 to stop, these circuits being similar to the corresponding circuit for relay CS2 hereinbefore described. When the crossover switches 33W and 3ASW have been operated to normal, the polar relay P3 associated with the control lever W for these switches will have its contacts closed to the left, and the polar relay P4 associated with the control lever G for signals L4 and R4 will have its contacts closed to the left or right, depending upon whether the direction of trafiic last established is for a train movement toward the left or toward the right. When the crossover is normal, relay CS4 may be energized over a circuit which may be traced either from terminal B, left-hand contact 3 of relay P4, contact I of the indication relay WK3 for the crossover switches, relay N3 associated with the crossover lever W, normal contact 5 of relay P3, lefthand contact 4 of relay P4, to wire 83 or from terminal B, right-hand contact 4 of relay P4, normal contact 5 of relay P3, contact 5 of relay N3, contact I of relay WK3, right-hand contact 3 of relay P4 to wire 83, and thence over back contact 4 of relay N4, front contact 2 of relay H4, front contact 5 of relay S4, relay CS4 to terminal C. These circuits may be closed to initiate a code to clear signal L4 or to clear arm a of signal R4, according to the position of relay P4, and thus function in the same manner as the circuits for initiating a code to clear a signal L2 or R2, but only when the crossover switches and their control lever are normal.

Relay CS6 may be energized by similar circuits to initiate a code to clear arm a or arm d of signal L6 or to clear signal R6, the circuits for relay CS6 including contacts i and 5 of the indication relay WK5 and the lever relay N5 associated with switch SSW, and in addition, including contacts 2 and '6 of relays WK3 and. N3 and the normal contact 4 of relay P3. It will be clear that these circuits for relay CS6 are available only when the position of switch ESW corresponds tothat of its control lever and the crossover switches and their control lever are normal. v

Arm 1) of signal R4 governs the movement of traffic over the crossover reversed, and relay CS4 may be energized to initiate a code to clear this signal by the closing of a circuit from treminal B, left-hand contact 4 of relay MKS, front contact 4 of relay N6, left-hand contact 4 of relay P6, wire 54, contact -5 of relay N5, contact I of relay WKli, reverse contacts 4 and 5 of relay P3, contact 5 of relay N3, contact i of relayWKt, right-hand contact 3 of relay P4, wire 83 and thence as already described through relay CS4, to terminal C. Front contact 4 of the lever relay N6 in this circuit closes when lever G for signals L6 and R6 is put to its stop position, but if the contacts of relay P6 are 'closed to the left, the established direction of traiiic'is toward the left and the signal put to stop is signal L8, this being the signal opposing signal R4 when the crossover is reversed, and the circuit will be held open until the approach locking associated with signal L6 is released to cause contact 4 of the corresponding indication relay MKB to close to the left. Relay P6 can be operated to the right only when signal L6 'is at stop and the approach locking associated with that signal is released, as will be clear from a consideration of the circuits for the similar relay P2 hereinbefore described in connection with Fig. 2, and if relay P6 has been operated to the right, the connection from terminal B over contacts 4 of relays MKS, N6 and P6 to wire 84 in the circuit just described are replaced by a connection from terminal B, righthand contact 4 of relay P6 to wire 8%. It follows, therefore, that relay CS4 can be energized to initiate a code to clear arm I) of signal B4 provided the lever controlling the crossover switches has been reversed and these switches have assumed the reverse position provided switch 58W agrees in position with its lever, and also provided the signal lever for controlling the opposing signal LG is in its stop position and this signal indicates stop and the associated approach locking is released.

It is to be understood in this connection that the control circuits are arranged as illustrated in the hereinbefore mentioned Kernmerer patent, in that the control circuit for each signal includes a front contact of the approach locking relay for the opposing signal and other contacts close when the switch or switches correspond in position with their control relays, so that the conditions governing the transmission of codes to control the signals correspond to the conditions governing their operation.

When relay P4 has been operated to the left, as shown, no circuit for relay CS4 including the reverse contact of relay P3 is available. It follows that when the crossover is reversed, the code for clearing signal L4 can not be initiated.

Arm b or arm (2 of signal L6, depending upon the position of switch 58W governs the movement of traflic toward the left over the crossover reversed. Relay CSB may be energized to clear one or the other of these signals by the closing of a circuit from terminal B, contact l of relayMK t, front contact 4 of relay N4, wire 83, over the right-hand contact 3 of relay P4, or from terminal B over the left hand contact 3 of relay P4 thence over contact of relay WK3, contact 5 of relay N3, reverse contacts 5 and 4 of relay P3, contact I of relay WK5, contact 5 of relay N5, wire 34, left-hand contact 4 of relay P5, back contact 4 of relay NE, front contact 2 of relay H6, front contact 5 of relay S6, relay CS6 to terminal C. A code for clearing arm I) or arm d of signal L6 may thus be initiated provided the crossover switches and their lever are reversed, switch 58W agrees in position with its lever, the opposing signal R4 and its lever are at stop and the approach locking associated with these signals is released. Furthermore, when relay P3 is reversed, there is no circuit for relay CS6 available if relay PS5 has been operated'to the right, therefore when the crossover is reversed the code for clearing signal Rt: can not be initiated.

It will be clear from the foregoing that'the circuits of Fig. 6 form a route network which is a counterpart of the track layout of Fig. 5, comprising circuits for each route completed by contacts of "polar stick relays associated with the switch levers and indicating the positions to which the switches have been operated, the integrity of these circuits being checked by contacts of switch lever relays N which when closed indicate that the polar contacts correspond in position to the switch lever and by contacts of switch indication relays WK which when closed indicate that the switches have been operated to a corresponding position, and furthermore that the direction of the flow of current in these circuits is governed by contacts of polar stick relays associated with the signal levers which indicate the established direction of traiiic, and that the route circuits are conable.

Considering now Fig. '7, relay WLS is the lock relay governing relay P5 associated with lever W for operating switch ESW and has a circuit which may be traced from terminal B, contact 1% of relays TK5 and MKE, contact 5 of relay Nfi, normal contact 6 of relay P3, relay WL5 to terminal C. Relay TK5 is the indication relay for section EDT and relays MK5 and N6, as already described, are associated with the signals governing the movement of traffic over section EDT. Contact 5 of relay P3 becomes closed to the left when the crossover lever W is operated to normal, and then the circuit for relay WLli functions in the same way as that of the corresponding relay WLZ of Fig. 2. Relay WLS is the lock relay governing relay P3 associated with lever W for operating switches 3SM and SA-SM and has a'circuit which may be traced from terminal B, contacts 3 of relays TK5 and MKE, contact 5 of relay N6, contacts 3 of relays TK3 and -MK4, contact 5 of relay N4,

relay W113 to terminal C. Relay TK3 is the indication relay for section 3DT and relays mm and N4 are'associated with the signals for that section, as already described. It follows that relay P3 controlled by relay WL? will be locked when section 313T or 5DT is occupied, or when any one of the signals of Fig. 5 has been cleared, or if either signal lever G is moved from its stop position. When relay P3 is reversed to close its righthand contact 6, relay WL5 has a circuit which, as is apparent from the drawings, is similar to that of WLB. Itfollows that when the crossover is reversed the lever locking conditions for switch '5SW are the same as those for the crossover, but 

